Strong zonation of benthic communities across a tidal freshwater height gradient

Abstract

Trade‐offs associated with environmental gradients generate patterns of diversity and govern community organisation in a landscape. In freshwaters, benthic community structure is driven by trade‐offs along generally orthogonal gradients of habitat permanence and predation—where ephemeral systems are physiologically harsh because of drying stress, but inhabitants are less likely to be under the intense predation pressure of more permanent waterbodies. However, in tidal freshwaters, these two stressors are compounding, and the trade‐offs associated with them are decoupled. We investigated benthic community structure in a tidal freshwater habitat. These communities experience a suite of conditions atypical for a freshwater habitat: twice‐daily drying; and high predation pressure by mobile fishes. We compared benthic communities at three tidal heights (low, mid, high) and contrasted these with nearby non‐tidal freshwaters that varied in their hydrology (permanent, temporary). We found that communities were more strongly differentiated in tidal freshwater habitats than between permanent and temporary inland freshwaters, which was surprising given the high interconnectedness and condensed longitudinal scale of tidal habitats. The differentiation of communities in tidal habitats was probably driven by the combined gradients of desiccation risk at low tide and intense predation by fish at high tide—a combination of pressures that are novel for the evolutionary history of the regional freshwater invertebrate fauna. Our study provides evidence that environmental gradients can produce stronger patterns of community zonation than would be predicted for habitats that are spatially contiguous and have little or no dispersal limitation. These results give insight into how communities might respond if drivers of community structure are altered or reorganised from their regional or evolutionary norms.

Contrasting Effects of Local Environmental and Biogeographic Factors on the Composition and Structure of Bacterial Communities in Arid Monospecific Mangrove Soils

“…The higher number of observed ASVs in Saudi Arabia, which is supported by higher phylogenetic diversity, may stem from the less favorable conditions for growth such as oligotrophy, higher levels of carbonates, high salinity, and extreme temperatures in the Red Sea ( 76 , 77 ). These conditions along with a small tidal range (0.2 m) in Saudi Arabia which may limit dispersal ( 78 , 79 ), can enhance the effects of environmental selection. Because we did not observe strong separation of bacterial communities at genus level among geographic regions suggests that evolutionary processes such as genetic drift or speciation may be in place ( 40 ).…”

Effects of Spartina alterniflora invasion on the benthic invertebrate community in intertidal wetlands

“…The patterns of zonation by invasive S. alterniflora have reshaped local landscapes. These intertidal gradients can control patterns of benthic invertebrate community zonation (McLachlan et al, 2019). In this study, we targeted an area of the YRD where an ongoing S. alterniflora invasion was occurring.…”